The ankle is a hinge joint formed by the articulations of the tibia, the malleolus of the fibula and the convex surface of the talus. Ankle injuries are relatively common injuries, particularly, as a result of athletic and sports activities.
The hind foot joints, including the metatarsal, the sub-talar and the talo-crural joints, function as a hinge to permit primarily up and down movement or bending (dorsi and plantar flexion). However, the joints also permit some turning in of the foot (inversion, a part of the supination movement) and turning out of the foot (eversion, a part of the pronation movement). The lateral malleolus (outside ankle prominence) tends to prevent excessive eversion (unless broken) but the medial malleolus (inside ankle prominence) does not prevent extended inversion to the same extent. Further the lateral (outside) ligaments are wider than medial ligaments and therefore the majority of ankle injuries occur to the outside or lateral side as a result of extended inversion.
Once severely sprained, the ankle joint is often weakened and susceptible to further injury and longer healing periods.
Taping the ankle is a common way to help protect an injured ankle but proper taping has a tendency to unduly immobilize the ankle and requires expertise that may not always be present, particularly if the tape is being changed by the injured person.
Ankle ligament protective devices or ankle orthosis are known in the art and have been developed in an attempt to provide proper support for the ankle without taping.
By way of example, Lindh et al U.S. Pat. No. 4,523,394, June 18, 1985 relates to a foot ligament protective device comprising a foot plate extending from a heel portion of the foot over at least the arch and an ankle sleeve provided with fastening means designed to be fixed around the ankle portion of the foot. Flexible, but not lengthwise extendable strap members are arranged to connect the ankle sleeve on both sides of the foot to the foot plate adjacent the heel and forward of the heel such that sideways overstretching movements of the foot are prevented.
More particularly, the Lindh et al device provides a connecting member which vertically connects the sleeve with the foot plate, the member extending generally vertically proximate the rear part of the foot plate and the heel of the foot. Another connecting member extends obliquely between the sleeve and the forepart of the foot plate. The connecting members permit foot movements through a normally full range of non-injurious positions but prevent excessive sideways movements into positions likely to cause ligament injury. The device can be worn with or without shoes.
The Paulseth U.S. Pat. No. 4,556,053, granted Dec. 3, 1985 also relates to an ankle orthosis useful for the prevention and/or rehabilitation of inversion injuries. The device includes a cuff adapted for fastening around the leg above the ankle, a foot plate for positioning beneath the foot, and connecting means extending down only the outer, lateral side of the orthosis (and foot). Resilient or elastic means may be used in conjunction with non-elastic means to produce any desired combination of elastic and non-elastic restriction of ankle inversion.
The abovementioned protective ankle devices give adequate support to the talo-crural joint but seem to have overlooked the stabilization of the sub-talar joint. Anatomically, the ankle joint is comprised of two distinct joints, those being the talo-crural and sub-talar.
The talo-crural joint is made up of the articulation between the inferior ends of the tibia and fibula and the superior articulating surface of the talus. The talo-crural joint is a compound, modified sellar joint. It has one degree of freedom; plantarflexion and dorsiflexion.
The sub-talar joint which is a compound, modified sellar joint is very important in that it allows for the inversion and eversion degree of freedom within the ankle. The anterior and posterior inferior facets of the talus articulate with the superior facets of the calcaneus to form the sub-talar joint.
The function of the sub-talar joint has been described by many authors. Downing, Klein and D'Amico state that ". . . , since no musculature attaches to it, the talus essentially functions as a `contoured ball bearing` allowing motion to occur concurrently between itself and the four bones with which it articulates" (Downing, J. W., Klein, S. J., D'Amico, J. C., The Axis of Motion of the Rearfoot Complex, J. Amer. Pod. Assoc., Vol. 68, No. 7, July 1978, 484-499). Therefore the talo-crural and sub-talar joints can be thought of as acting together as a functional complex.
It is known by those in the field that the combination of ankle inversion (sub-talar joint) and plantar flexion (talo-crural joint) during bearing leads to a typical ankle sprain.
Accordingly, there is a need for a new orthosis device which will adequately stabilize the sub-talar as well as the talo-crural joints of the ankle and prevent inversion of the ankle with minimal limitation to, other movements within the joints including plantar flexion.